This invention relates to a mobile communication device for use in a spread spectrum communication of code division multiple access (CDMA) system.
In general, it is necessary to reduce a tracking error between a reception signal and a reference signal in a mobile communication device of CDMA system. The mobile communication device comprises a synchronous tracking circuit for carrying out a synchronous tracking between the reception signal and the reference signal. A delay locked loop circuit may be used as the synchronous tracking circuit. A conventional delay locked loop circuit comprises a first generating section for generating an early signal and a first late signal and will be referred as a first conventional delay locked loop circuit. The phase of the first late signal is later in one chip delay than that of the early signal. The first conventional delay locked loop circuit reduces the tracking error between the reception signal and the reference signal in accordance with the early signal and the first late signal, as will be described later.
Furthermore, a conventional delay locked loop circuit comprises a second generating section for generating the early signal and a second late signal and will be referred as a second conventional delay locked loop circuit. The phase of the second late signal is later in two chip delays than that of the early signal. The second conventional delay locked loop circuit reduces the tracking error between the reception signal and the reference signal in accordance with the early signal and the second late signal.
In the first conventional delay locked loop circuit, a following range of synchronization is narrow although the tracking error is small. It is difficult to make the following range of synchronization be wide in the first conventional delay locked loop circuit. As a result, a pull-out often occurs in the first conventional delay locked loop circuit.
In the second conventional delay locked loop circuit, the tracking error is large although the following range of synchronization is wide. It is difficult to make the tracking error be small in the second conventional delay locked loop circuit. As a result, it is difficult to correctly carry out a tracking precision.
It is an object of this invention to provide a mobile communication device having a good tracking precision and a wide following range of synchronization.
Other objects of this invention will become clear as the description proceeds.
On describing the gist of this invention, it is possible to understand that the present invention is a mobile communication device having a delay locked loop circuit for carrying out a tracking synchronization of a reception signal. The reception signal may be a spread spectrum signal.
According to this invention, the delay locked loop circuit comprises generating means for generating an early signal and first and second late signals which are different in phase from one another, multiplying means for multiplying the reception signal by each of the early signal and the first and the second late signals to produce first through third multiplied signals, producing means for producing a tracking error signal in accordance with the first through the third multiplied signals, and supplying means for supplying a clock signal to the generating means on the basis of the tracking error signal to make the generating means generate the early signal and the first and the second late signals.